1. Field of the Invention
The present invention relates to a method of packaging a semiconductor device. It finds particular utility with devices such as image sensors, MEMs, and pressure sensors.
2. Description of the Related Art
Semiconductor sensor packages generally include a semiconductor die part that is mounted on a substrate made of metal or plastic or a combination thereof, with the die and substrate being enclosed within a plastic material. However, since sensor semiconductors must be capable of being exposed to, e.g., light, in the case of optical sensors, or a fluid, in the case of pressure sensors, the active die surface must be left exposed, or at least accessible, after the die and substrate have been enclosed.
Prior art packaging techniques often use a ceramic substrate material, which is preconfigured with a cavity to accept the die. Such ceramic substrates are in single unit form, they cost more than substrates made of metal or plastic or a combination thereof.
Once the die is attached to the substrate, a cap is applied to protect the die surface and to seal the unit. Prior art techniques attach a cap to the substrate, the leadframe or the die surface. The cap is held in place using an adhesive. The adhesive is usually in the form of a paste or it is dispensed from a tape. However, the application of adhesive in either form is difficult, prone to result in adhesive being erroneously applied to the die surface and requires lengthy periods for the adhesive to cure.
Another technique which is used to protect the die surface while the package is enclosed in a molding material uses a soft deformable insert that is placed over the die while molding material is injected to enclose the entire package. Later, once the molding material has set, the insert is removed, leaving a raised edge of molding material around the die. However, there is a risk that the delicate die surface can be damaged by the insert either at the preparation or the removal stage. Insertion and removal are also additional steps in the manufacturing process that require more time, additional machinery, and increase the opportunity for error.